This invention relates to a unique method and device for purification of sewage, wastewater or potable water by thin film aeration and a special prefilter, described in Vandervelde and Helm's U.S. patent application Ser. No. 404894, filed Sep. 8, 1989, now U.S. Pat. No. 4,997,568.
Historically, water purification has taken advantage, in some cases, of aerobic or anaerobic biological devices to produce improved effluent using biota fixed on a substrate, or suspended. Anaerobic devices have traditionally been limited to a maximum of about 70%-80% treatment and proposed as polishing stages prior to some further action, as in E. J. Jordan's (U.S. Pat. Nos. 3,950,252, Apr. 1976 and 4,211,655 Jul. 1980), A. A. Monson's (U.S. Pat. No. 4,162,976 Jul. 1979), and A. W. Green's (U.S. Pat. No. 4,293,421 Oct. 1981).
Sewage and wastewater disposal is becoming a bottleneck in providing housing and employment for an increasing population. As sewage treatment standards become stricter and availability of clean water more restricted, the cost of providing these services rises. The result is people with substandard or unavailable housing and employment in many communities.
Extending and constructing standard municipal sewage plants to accommodate higher population densities is environmentally unsound and becoming cost prohibitive. These systems use poisonous disinfectants, pollute the surface water into which they discharge and prevent normal beneficial recharge of aquifers.
Standard on-site septic systems, to work well, require special soil and groundwater conditions with large lot sizes. These factors are also becoming less available and more expensive as development proceeds. They discharge incompletely treated effluent into the environment.
More exotic and costly on-site septic systems designed to treat sewage under poor soil and groundwater conditions are being used to fill the gap. These include Wisconsin Mound Systems, sand filters and a proliferation of types of mechanical aerobic reactors, many of which use chemical disinfectants that repollute their effluent. These expensive systems do a passable job if designed, installed, and maintained properly. However, they seldom are because of their inherent complexity. This results in discharge of untreated or poorly treated sewage to pollute ground and surface water. Pumps and other mechanical devices that they require are often beyond the owner's financial capability, or interest, to maintain.
Commonly used sand and gravel filters rely on mechanical devices to increase the air/sewage interface by spraying, sparging, or spreading it over sand, gravel, or soil beds. This allows the growth of aerobic biota which treat the sewage. One of the most advanced and effective examples of this type is covered by U.S. Pat. No. 4,251,359, currently merchandised by SPEC Industries.
While investigating ultra-thin water film formation, we found that sewage caused to flow in a film over a hydrophillic surface, such as cotton cloth or sand, left its impurities behind and could then be released by gravity in liquid form into a collector. This resulted in a pooled, pure product free of odor and contamination while freeing the medium surface to adsorb more film.
We believe that further review of patents and literature will not reveal a method or device which can accomplish this treatment as we have. Advantages of this invention are submitted in the Summary.